Shaped laminated composite parts may be laid up ply-by-ply on a tool referred to as a mandrel. The mandrel has a tool surface substantially matching the part which functions to shape the plies as they are laid up and compacted on the mandrel. In those cases where the tool surface is highly contoured and the layup is wrapped at least partially around the mandrel, the layup may become locked on the mandrel, making release and removal of the layup difficult.
In order to facilitate layup removal, mandrels have been devised that partially collapse or at least contract enough to change the shape of the mandrel. This change in shape creates a clearance between the tool surface and the layup that is sufficient to “unlock” the layup and allow it to be removed from the mandrel. One known type of collapsible mandrel requires the insertion of an expander into the interior of the mandrel. The expander comprises inclined blocks which engage opposing interior walls of the mandrel. Manual rotation of a threaded rod passing through the blocks causes the blocks to expand and apply outwardly directed pressure on the mandrel walls. The blocks are used to slightly expanded the mandrel so that a portion of the mandrel, sometimes referred to as a tool block, can be removed. With the tool block removed, the mandrel partially collapses to create the clearance needed to the release the layup.
The use of the expander described above may have several disadvantages. For example, the expander is relatively heavy and awkward to manipulate, requiring at least two operators to install and operate. Also, the installation and removal of the expander is time consuming, and its reliability is less than desired.
Accordingly, there is a need for a layup mandrel that includes a mechanism for changing the shape of the mandrel to allow removal of a ply layup, which allows quick layup release, is easy to use and reduces dependency on manual labor.